In the production of seamless tubing, a cylindrical metal workpiece is advanced over a piercing mandrel, by means of a pair of heavy rolls, arranged at a slight angle to the axis of the workpiece. In accordance with well known principles, the heated workpiece is simultaneously rotated and advanced in a manner to enable it to be driven over a piercing mandrel and formed into a tube. After one or more such piercing operations, the tubing is passed through a plug mill for sizing and then through a reeling mill. The reeling mill serves to rapidly rotate tubular stock about a mandrel, while simultaneously advancing the stock, in a manner calculated to impart greater roundness and uniformity to the cross section.
Because of the need for refurbishing of the rolls, provision is made for bodily removal of roll modules from the mill structure, as may be necessary from time to time. In a typical piercing or reeling mill, the mill rolls are arranged generally on opposite sides of the pass line axis, on the same general horizontal level. Inasmuch as substantial forces must be contained during operation of the mill, the frame structure for supporting the roll modules is extremely heavy and sturdy. To permit occasional removal and replacement of the roll modules, typical construction of piercing and reeling mills includes arrangements for the removable securement of a frame member, customarily referred to as the cap, which extends across the top of the frame and joins the tops of the upright frame members spaced on opposite sides of the pass line. In keeping with the overall construction requirements of the mill frame, the cap members are necessarily of extremely heavy, massive construction.
In the past, in order to effect a change of working rolls in the mill, removal of the mill cap has been accomplished by bringing the plant crane into position over the mill, and bodily lifting and carrying away the cap. Not only is this a relatively hazardous operation, but must be done with great care and results in the utilization of substantial working time of the plant crane. An inevitable result is that the overall task of changing mill rolls consumes an inordinate amount of time and significantly reduces the overall efficiency of utilization of the mill, which is an extremely high capital cost installation, as will be appreciated.
In accordance with the present invention, improved arrangements are made for the mounting and support of the mill caps for piercing and reeling mills, enabling the mill caps to be removed quickly and without the intervention of the plant crane, thus significantly expediting the roll changing operation. More particularly, the mill construction is such that the cap structure is self-supported on extensions of the mill frame, and the mill structure is provided with self-contained means for effecting lateral movement of the mill cap from its normal working position, in order to provide overhead crane access to the mill roll modules.
In one advantageous form of the invention, the mill cap is slideably supported and guided on the mill frame uprights, and lateral extensions thereof, providing for accurately guided sliding movement of the cap into a laterally offset position to provide access to the mill rolls. In conjunction therewith, the slideable guide ways, cooperatively positioning the cap and the mill uprights, are slightly tapered in a direction such that, when the cap is moved in a mill-opening direction, free sliding clearance is provided whereas, when the cap is returned in the mill-closing direction, the guide clearance is closed and the cap is forced into a precise alignment. Heavy-duty, quick releasing clamp means are provided for securing the cap in its mill-closing position to provide an effectively unitary mill frame suitable for supporting the mill rolls against the heavy forces of the rolling operation.
In another advantageous form of the invention, double acting fluid actuator means are provided which, in one condition, serve to rigidly clamp the cap in its mill-closing position. In the other condition of the double acting fluid cylinders, the cap is raised up off of the vertical supports and is supported in a mobile fashion on track-supported wheels, enabling the cap to be easily moved off to the side to provide overhead access to the mill rolls.
In either of its forms, the mill structure of the invention greatly expedites the process of mill roll exchange and thus substantially improves the capital use efficiency of the mills.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of preferred embodiments and to the accompanying drawings.